5m now in 10 days meaning it moved another 1m in the following week.
I believe this already makes it the best selling Monster Hunter among those that were only released on a single platform. Obviously, it still has a long way to go to get near MH World numbers. However, after that Capcom has the next best selling MH at 4.9m, Monster Hunter Freedom 3 on PSP.
Rise is definitely getting a lot of benefit from World's popularity.